Engine starting device



Feb. 28, 1933. s, c us 1,899,229

ENGINE STARTING DEVICE Filed April 30, 1952 2 Sheets-Sheet l Feb. 28,1933. P s, CLA 1,899,229

ENGINE STARTING DEVICE Filed A ril 30, 1932 ZSheets-Sheet 2 the pinionis rotatively locked upon the Patented Fe'b.: 28, 1933 A-TEINT,QFFICE I.A

new s. CLAUS, or DETROITLMICHIGAN Y i iE NG I NE S ARTING-DE CE; y

,nil i'canon nlea s ruce, 1932. Serial nmsoasoa My=invention relates topower drives and consists, more particularly, man improved automaticstarter drive for'cranking internal combustion engines. 7 I

The niostcommon and satisfactory starterdrive forinternal combustionengines now on the market consists essentially of'aworm or threadedmembe rrotative1y driven by the starter motor, apinion gear threadedly.

associatcdfwith said worm and projectable thereon, by means of itsinertia,into engagement with the engine, gear, anda stop element at theend of the worm againstwhich A the pinion abuts when projected, and bywhich worm member. In this construction the pinion is projectedwitlirespect' to the worm and its projective movement issuddenly'brought to an instantaneous and complete stop, si multan-eously"positively lockingit upon the WOI'IH to pick :up the entire load ofcranking the engine. Because of the terrific shock inherently incidentto the instantaneous stopping of the pinion and picking up (of the load,7

some sort of shock absorbing 'or cushioning means is an absolutelyessentlal element in a satisfactorydevice embodying this construc tion.The conventional cushioning means employed consists of an expandedspiral sp'ringthrough which the drive is yieldingly transmitted,and bywhich a c'ertain'amount of longitudinal movement of the worm ispermitted; Theincorporation ofthe spring does M not preclude oreliminate the. shockit serves merely to mitigate an objectionablecharacteristic inherent in this type of device. I

With this and other undesirable features of the prior art devicesinxmind, my invention has certain well defined objects, A-

vide a starter drive in which the pinion is described.

accurately centered upon its shaft to the elimination of thenoise,;wear," and loss of power incidentto misalinement of pinion gearand engine gear.

Another object of my invention is top'rovide'a starter drive in whichfacile-meshing ofthepinion and engine gear is assured and burring of theteeth thereof is precluded;

vide a starter drive which rele'ases with ease, and which is not subjectto the sticking so common with prior starter drives of the type Anotherobject of myinvention is to provlde a starter drive-in which the piniongear Another objectofmy inventionis to proautomatically overruns the.starter motor shaft in the event that the engine kicks or runs'backward, thus precluding excessive discharge ofthe battery, breakageor bend v ing of. the drive shaft, stripping of gear,

teeth; orother injury.

Another object of my inventionis to pro videa'shockless starterdrivegwhich imparts a rotation to the engine crankshaft which is a truefunction of the rotation of the, starter motor, that is, a crankingmovement "without; the usual periodof deceleration due to momentarywindup Of-"jih drive-cushioning springeach time'an'ienginecylinderisunder- I going the compression'cycle Such a'cranking'movementfireefromsuch periods ofdef- 'celeration, ;,closely approximates the'snappyactioncharacteristic of effective handcrank- 'ing as practiced byskillful inotoristsin the days before the electric starter;

' Another object of my inventionis to provide a starter drivewhichissimple, which is not subjectto wear or breakage, whichmaycheaply-manufactured by production: methods, ofautomatic stamping andmachining, and which may be assembled by un-v skilled" workers in afraction of the time now required to assemble prior art starting drivesofthe conventional type described."-

"Further objects," and objects relating-to details and economies of 1construction 1 will 1 'definitly appear from the detailed description tofollow; Inone' instance I accomplish the objects of my invention by" thedevices] and means eset fo'rthin the following 'specithe appendedclaims. Structures constituting preferred embodiments of my inventionare illustrated in the accompanying drawings forming a part of thisspecification, in which:

Figure '1 is a view in side elevation, of a preferred form of starterdrive embodying my invention, fragments only of the starting motor andengine ring gear beingshown to illustrate the relationship ofthe partswhen not in operation;

Fig. 2, is a vertical sectional view of the same starter drive;

Fig. 8 is a transverse sectional view taken on the line 3-3of-Fig.2; YFig. 4 is a transverse sectional view taken on the line 44 of Fig. 2;

Fig. 5 is a perspective view clutch member Fig. 6 is a'view insideelevation, of a modified form of starter drive embodying my invention,fragments only of the starting motorand engine ring gear being shown toillustrate the relationshipv of the partswhen not in operation;

Fig. 7 is a vertical sectional view 'ofthe starter drive shown in Fig.6;

Fig. 8'is a transverse sectional viewftaken f the; locking on the line8+8 of Fig; 7;: f

Fig. 9 is a transverse sectional view taken on the line 9&9 of Fig. 7; I

Fig. 10 is a detail view of a portion of one of the clutch members,showing the spaceproviding lugg'and Fig. 11 is a detail viewof a portionof the other clutch member constituting ,a part of the device shown inFig. 7, showing the lugreceivi-ng notch.

Like reference numerals. refer to-similar parts throughout the severalviews.

In itsbroad sense, 'myinvent-ion comprises an engine starter driveincluding a starting motor driving a shaft upon which are mount .ed apair of differentially threaded screw members or worms, the threads ofwhich turn in the same direction but are of diiferent lead .or pitch.Carried by the threadedgmember oflesser pitch is a pinion, preferably asmall gear having teeth of the'same pitch as the .teethof a largeringgear'on the flywheel of the engine.

This pinion has a thread or -threads which are associated with thethreads of the" threaded member of lesser pitch and which cause thepinion to move longitudinally into mesh with the ring gear whenthethreaded member is revolved by the starting -motor, and the pinion, byreason of its inertia,i is overrun. {Carried by the threaded .member ofgreater pitch is a clutch member which, like the pinion, isprojectediinlthedi- .rection of the ring gear when the associated threaded member.overruns the clutch member due to inertia of the latter. The clutchmember and pinion are, when inretracted threaded member of lesser pitchis journaled upon the drive shaft and rotates in unison with thethreaded member of greater pitch solely by reason of frictional couplingtherewith. When the clutch has, by reason of its greater rate ofprojection, overtaken the still projectively moving pinion, aprogressive binding action is initiated and the clutch and pinioncontinue'tomove as aunit on their respective threaded members, becomingmore and more tightly wedged upon themselves and the threaded members byreason of the differential threadingthereof, binding the threadedmemberof lesser pitch,.if of the floating type, upon the drive shaft and theother threaded member, gradually picking up the load and continuing theprogressive binding action, while more and more load is being picked up.Thus it will be seen that there is no positive stop in the presentconstruction, no locking of the pinion to start the cranking action asin the drives heretofore known, but a gradual, progressive binding ofthe pinion upon several members, which binding-is proportional to theload being undertaken. The pinion has nodefinite limit of projectivemovement as positively determined by the elements of other devices forperforming cranking operations, but to the contrary, travels on itsindividual worm a distanceproportional to the load undertaken. V

Referringnow, more particularly, to the preferred embodimentzof my,invention illustrated in Figs. 1 to 5 of the drawings, my starter drivecomprises a drive shaft 10 driven by the. starting motor 11, upon whichshaft are'mounted a pair. of differentially threaded sleeves or worms12-and 13. The outer sleeve 12 is keyed, pinned or spliried to the driveshaftlO as bymeans of a key 14. If desired, the assembly .collar 15secured to the end of the shaft 10 by a pin 16 may be formed integralwiththe worm sleeve 12 and the key 14 may be omitted. At the other endof the driveshaft 10, adjacent the motor 11, is provided a thrust collar17 secured thereto by means of a pin 18, and the worm sleeve is.journaled between the collar 17 and worm 12.

the teeth'20c' of the flywheel ring; gear 20 of the enginetnotgshown).The pinion 19 has threads 19?) which are associated with which-cause thepinion to travel-toward the ring gear 20when'the worm 13 is rotatedbythe starting motor. At the outer end of the pinion is formeda' conicalclutch portion 190' within which the complementary conical clutch face21?) of the clutch member 21 is receivable. Clutch member 21 is carriedby the worm sleeve '12 and has threads 21a which are associated withthe'threads 12a of the wormsle'eve 12, and which cause the clutch member21 to be projected toward the ring gear 20 when theworm sleeve-12 isrotated by the motor 11. Worm sleeves 12 and 13 are differentiallythreaded, that is their threads 12wand'13aturn in the same direction,but the threads-12a have greater lead' or pitch-than the threads-13a, Innormal in-' operative position the clutch member 12 is speedofprojection, overtakes retracted adjacent the collar 15 and the pinion 19is retractedto the limit defined by the unthreaded end 1365 of the wormsleeve 13. In these retracted positions,;the clutch face 21?) of theclutch-member 21 is spaced from the clutch face 190a distancesufficientto-ah low the pinion 19 to 'mesh with the'ring gear 20asubstantial distance before the clutch member 21, by reason of itsthreads 21a .of greater pitch and its consequent greater and binds thepinion 19to transmit torque. For the purpose of maintaining a fairlyaccurate timing for this binding action so that proper meshing of thepinion and ring gears is assured,

as well as for the purpose of eliminating any tendency of the pinion '19to accidentally roll down the worm sleeve13 into engagement with thering gearQO'when theengme 18 not level, a collar 22 is pressed ion theclutch member 21 and loosely-ties the clutch memher and pinion '19against becoming widely. "separated. Slots 23 arepreferably formed 7 inthe face 21?) of the clutch me1nber-21,which slots'pe'rmit more accurateconformity of the face 21?) to the pinion face 19c-and provide smootheraction.- e I 1' The operation of the deviceis extremely simple. When thestarting motor 11 is energized, the shaft 10 is revolved, viewing theouter end of the illustrated embodiment, in a c0unter-clockwisedirection. Wormsleeve 12 is, byreason of its keyed relation tothe shaft,rotated counter-clockwise, as isworm sleeve 13, by reason of itsfrictional association withshaft 10, collar 17 and sleeve 12;

Pinion gear 19 andclutch member 21, by reasoniofxtheir inertia, do notinstantly start I 13 tor end of the shaft 10. Pinion, 19, beinginitially spaced from clutch member 21, is

projected upon its worm 13 until it"is well been demonstratedexperimentally by manmeshed with ring gear-2O before it is overtaken bythe morer'apidly projected clutch lniember21. The two elements, clutchmemthe threads2x13aof.the wormlsleeve' 13 and to bind and tend to rotatewith the drive shaft .10. The tendency'to bind isapro- 'gressive action,very lightat the start, due,

her and pinion, having: contacted, now begin and'19c is aprogressive andjoint windingup -of clutch member and pinion upontheir ing of theseveral parts;'worm sleeve 13 with collar- 17; pinion threads 1% withworm threads 13a; clutch threads 21a with. worm threads 12a; and'clutchface 21bwith clutch pinion 19 and clutch member 21 may turn with respectto drive shaft 10, under heavy load, nearly a complete revolution afterinitial contact of faces 21?) and 190 has taken place: I consider'thisprogressive load take: upfeature of my invention tobe a revolutionarydeparture from all other systems for accomplishing the cranking ofinternal com- 3 bustion engines. I h

I The disengagement of the pinion 19 from the ring gear 20, when theengine starts, is as quiet and easy as is the engagement, At thefirsttendency of thepinion to overrun the drive shaft 10, thepiniontends to wind 'rearwardly upon the rworrn threads 13a; Dueyto thefrictional engagement of clutch face 190 withclutch face 211), clutchmember:

190 is broken and the parts return to their retracted, normally spaced:relation defined with: which disengagement is effected has ually settingthe parts in driving-relation, clamping the pinion in a vise, andtightening the drive shaft with an eighteen-inch pipe wrench until nofurther binding could be effected by manual pressure'upon the wrench.The drive, still" thus engaged, was removed from the vise,andby'grasping the'drive shaft in one hand, and turning thepinion gearwith the other hand tolsimulate start- I ingpof the engine, theengagement was broken with but the barest effort. A very." importantfeature of my device is itsunique action when, due to excessivelyadvanced ignition, "the engine kicks or 1 runs backward instead ofstarting. Undersuch 21 tends to rotate with pinion 19 and, dueto thegreaterpitch of its threads, once started to overrun shaft 10, contactof faces 21?) and no bycollar 15 and'worm end 13d. The ease respectiveworms, effecting a gradual bind- I face/19m Actual observationdisclosesthat" I conditions, the pinion 19, instead of remain ing lockedupon thedrive shaft, as in:the

case of conventional starter drives, causes the floating worm member 13to slip upon the drive shaft, and the clutch face 190 of the pinionitself slips-upon the clutch face 21?) of the clutch member 21 withouteffecting any material separation therefrom or projection of the piniontoward the stating motor. lVhen the engine ceases to violently reactagainst the drive, and the drive is resumed by the starting motor, theclutch-member is slightly further projected and the progressive grindingaction again takes place, tothe resumption of the cranking op- 'eration.

It is to be noted that, by reason of the engagement of the conical'faces 21b and 190 of the clutch member and pinion, the latter iscentered upon the drive shaft so that ofthe pinion with the engine gearis so slight as to hardly be audible over the sound of the engine.Moreover, careful examination of the pinion and engine ring gears aftersuch abuse, long continued, failed to reveal even the-finest scratch oneither gear.

In Figs. 6 to 11, I have disclosed a modi fied form of my invention inwhich the threaded members or worms are not similar, one being internaland the other external.

As in the first illustrated embodiment, however, the essential featuresof differential threading, and spacing of clutch and pinion to effecttimed, progressive; binding after meshing of pinion with engine gear,are prescut. I In this modified form, there is a drive shaft--10 drivenby the motor 11, a thrust collar 17 secured to the drive shaft adjacentthe motorll by means of a pin 18, a floating worm sleeve 13 having itsforward end 130 abutting the collar 17 and held adjacent thereto by asplit ring .336, a pinion gear 39 threadedly associated with the wormsleeve 13, limited in retractive movement by the end l rlof the wormsleeve, and having a clutch portion 390. Upon the rear end of the driveshaft is pinneda cup-shaped member .32, internally threaded in the samedirection as worm sleeve 13 but having threads of greater pitch. WVithinthe threaded member 32 is disposed the end of a clutch member 41 hearingthreads 41a which are engaged with those 32a of the member .32. Themember 32 isprefe'rably recessed at 325 to preclude any tendency'of themember 41 to stick when retracted to the limit of its movement. Upon.the forward endof clutch member 41 is carrieda slightly conical'frictionWasher 416 which is normally spaced from the clutch face 390 of thepinion when the parts are in retracted position. For the purpose ofpreventing the clutch member 11 and pinion from becomingtoo widelyseparated, as well as for eliminating any tendency of the pinion to rollupon its worm member when the engine is not level, there are providedlugs 42 on the washer 41b which are received loosely in notches 42a inthe pinion clutch portion 390. Due to the fact that the spacing of thewasher 41b and portion 390 is slight, jthe -.relative rotationtherebetween necessary to effect their contact is slight, and thenotches 42w need not be much wider than the lugs 42. In order to permitslippage in the event of kicking or running backward of the engine, thewasher 41b is snuglyjournaled on the clutch body proper and is held inassembly therewith bythe split ring 410.

The operation of the device illustrated in Figs. 6 to 11 issubstantially the same as that shown in Figs. 1to 5. Rotation of shaft10 by the motor 11 causes pinion 39 to engage engine ring gear 20.Clutch member 4:1 is at the same time moved toward pinion gear 39, anddue to the greater pitch of the threads 32a of member 32, Washer 41?;overtakes the clutch face of pinion portion 390 shortly after theengagement of pinion 39 with ring gear 20. Progressive binding action ofthe several parts is then initiated and continues, gradually picking upmore and more of the load, as in the case of the device illustrated inFigs. 1 to 5.

I amaware that my invention is capable of numerous embodiments, the twodevices illustrated being merely illustrative. Likewise, numerouschanges might be made in the illustrated devices. (For example, thepinion-associated worm sleeve 18 might take the form of an internallythreaded member; also, it might be keyed to the drive shaft 10,although, in practice, Ihave found it desirable, from the standpoint ofease of engagement and disengagemenq as well as accommodation ofenginekick, to have this part merely frictionally associated with thedrive shaft orother threaded member. For the purpose of increasing itscoefficient of friction, a spring may be provided on shaft 10 toinitially. urge collar 130 more tightly against collar 17. Numerousforms of clutches are available as-equivalents of those illustrated,although .I prefer conical faces thereon because of the centering effectthey have upon the pinion gear. In actual practice, I have foundthat'the space-limiting members 22 or a2 and 42a are not essential, theparts normally tending to assume and 7 remain in properspacedrelationship and offer no in terference with the ring, gear 20; Theslots 23 in the clutch member forming a part of the device illustratedin Figs. 1 to 5 arelike wise not essential to the invention, adequateengagement being attainable without them."

I believe the concept of provid'inga self-governing; progressive drivefor performing cranking of IIItGIIlfiLGOIIlbllStlOD engines andlikefunctions,-which progressive drive is ef-i fected by theaction of apair of differentially threaded members, is a revolutionary-step 1. Inan engine starter "drive, the combination of" a pair of jalineddifferentially threadedmembers, the onehaving threads of "greater pitchbeing rotated by the prime mover, and the one of lesser pitch beingrotatable in unisonwith the threaded member of greater pitch, adrive-transferring pinion carried by the threadedmember of; lesser pitchand having threads engagedtherewith eflective, When' overrun by {the"associated threaded member, to project saidpinion intodrive-transferring engagement with the en'- gine to be driven andeflective', when the pinion 'overruns the associated; threaded mem--ber,-: to retract said pinionffrom said drivetransferring engagement,and a clutch member carried by said threaded member of greater pitchandnormally spaced from clutching enga ement with said i'pinion, said jclutch mem er having threads engaged with those of the member by whichit is carried-and effective, when overrun by j its associated member, toovertake, clutch, and travel with said pinion member after the'latterhas been projected so that by the differentially threadedcharacter of the threaded members the several parts will beprogressively bound together for rotation as a unit. J 2. In an'enginestarter drive, the combination of apair of alined diflerentially thread-7 ed members, the one havingthe threads of greater pitch being; rotatedby the prime mover and the one of lesser pitch being r0- tatable i'nunison withthe threaded member of greater pitch, a drive-transferringpinion carried by V the a threaded member oi /lesser pitch andhavingtheads engaged therewith effective, when overrun by the associateddrive-transferring engagement with the engine to be driven andeffective, when 'thepin ion overruns the associated threaded member, toretract saidpinion from said-drive-tra-ns ferring engagement, 1 and aclutch member carriedby said threaded member'of greater pitch, saidclutch member having "its clutch faceof conical form, normally spacedfrom but en ageable with a complementary portion, 0 said pinionwherebyrcente'ring and alinement'of the latter with respect to theaxisof rotation is assured, said clutch memberhaving threads" engaged withvthose of the member'by which it isicarried andeflective, when overrunbyits associated member,

to overtake and engage its conical face with the complementary portionOfsaidpinion" after the latter has been projected so that by thedifferentiallythreaded character of I the threaded members the severalparts'will be progressively bound together for rotation as a unit.

'3. In an engine starterdrive, the combina tion of a drive shaft, a pairof alined differentially threaded members thereon, the one'having thegreater pitch being rotated by the'drive shaft,and the other being ro-"tatably journaled upon the drive shaft and frictionally'ass'ociatedtherewith so as to nor-f mally; rotate vin unison with the threaded:

member of greater; pitch, a drive-transfer? rlng pinion carried by thethreaded member of lesser pitch and having threads engaged, therewithefiective, when overrun by the as socia-ted threaded member, to projectsaid pinion into drive-transferring engagement with the engineto bedriven and effective, when the pinion overruns the associated threadedmember, to retract-said pinion from, said drive-transferr ng engagementand a clutch member car'ried by said threaded member of greater pitchand normally-spaced from clutching engagement with saidpinion,

said clutch member'having threads, engaged:

with those of the member'by which it is carried and effective, whenoverrun by its associated" member, to overtake, clutch, and

travel with said pinion member afterthelatter has'been projected so thatby the differentially threaded character of the threaded members theseveral parts Will be progressively bound together for'rotation asaunit.

4; In an engine starter drive, the combi nation ofa drive shaft, a pairof alined differ'entially pitched screwsleeves thereon, the onehavingwthe greater pitch being rotated by the drive shaft, and-the oneof lesser pitch being rotatable in unison with the screw sleeve ofgreater pitch, adrive-transferring pinion carried by the screw sleeve oflesser pitch and having threads engaged therewith effective, whenoverrun by the associated screwsleeve, to project said pinion'intodrivetransferring engagement with the-engine to threaded member, toproject said pinion into be drivenand efiective, when the pinion'ov'er'runs the associated screw-sleeve, to retract said pinion from saiddrive-transferring engagement, and a clutch member carried by said screwsleeve of greater, pitch and nor-, mally spaced from clutchingengagement with said pinion, said clutch member hav a ing threadsengaged withthe screw sleeve by which it is carried and effective, whenoverrun by its associatedsorewsleeve, to overtake, engage, and travelwith said pinion after the latter has been projected, so that by thedifferentially pitched character of the screw sleeves the several partswill be progressively bound together for rotation as a unit. a

5. ;In an engine starter drive, the combination'of a drive shaft, a pairofalined differentially pitched screw sleeves thereon, the one havingthe greater pitch being rotated by the drive shaft, and the one oflesser pitch being rotatably journaled upon the drive shaft andfrictionally associated therewith so as to normally rotate in unisonwith the screw sleeve of greater pitch, a drive-transferringpinioncarried by the screw sleeve oflesser pitch and havingthreadsengaged therewith efiective, when overrun by the associated screwsleeve, to project said pinion into drivetransferring engagement withthe engineto be driven and effective,when the pinion overruns theassociated screw sleeve, to retract said pinion from saiddrive-transferringengagement, and a clutch member carried by said screwsleeve of greater pitch and normally spaced from clutching engagementwith said pinion, said clutch member having threads engaged with, thescrew sleeve by which it is carried a-ndefiective, when overrun by itsassociated screw sleeve, to over take, clutch, and travel with saidpinion after the latter has been projected, so that by thedifferentially pitched character of the screw sleeves the several partswill be progressively bound together for rotation as a unit.

6. In an engine starter drive, the combination of a drive shaft, a pairofalined difl'erentially threaded members thereon, the one having thegreater pitch being positively driven by the drive shaft, and the one oflesser pitch being rotatively associated to normally rotate in unisonwith the threaded member of greater pitch, a drive-transferring pinioncarried by the threaded member of lesser pitch and having threadsengaged therewith effective, when overrun by the associated threadedmember, to project said pinioninto drive-transferring engagement withthe engine to be driven, and effective, when the pinion overruns theassociated threaded member, to retract said pinionfromdrive-transferring engagement, a clutch member carried by said threadedmember of greater pitch and having threads engaged with those of thememberby which it is carried, and means associated with said pinion forproviding apredetermined amount of spacing between said pinionand saidclutch member when in r'e tracted positions, so that Whenoverrunby.

their respective threaded members, the pinion willfirst be projectedinto drive-transferring engagement withthe engine and said clutch memberwill, by reasonof the greater pitch of its associated threaded ;member,overtake,engage, and travel with said pinion member so as toprogressively bind the sevbeing rotatively1 associated to normallyrotate in unison with'the threaded member of greater pitch,'adrive-transferrmg pinion carried bythe threaded member of lesser pitchand having threads engaged therewith effective, when overrun by theassociated threaded member, to project said pinioninto-drivetransferring en agement with the engine to be driven, andefiective, when the pinion overruns the associated threaded member, toretract said pinion from drive-transferring engagement, a clutch membercarried by said threaded member of greater pitch and having threadsengaged with those of the member by which it is carried, and meansassociated with said pinionfor providing-a predetermined amount ofspacing between said pinion and said clutch member'when in retractedpositions, so that when overrun by their respective threaded members,the pinion will first be projected intodrive-transferring engagementwith the engine and said clutch member will, by reason of the greaterpitch of its: associated threaded member, overtake, clutch, and travelwith said pinion member so as to progressively bind the several parts ofthe device together for rotation as a unit, said spacing meansincluding'a stop for limiting the extent of retraction of the clutchmember, a stop for limiting the extent of retraction of the pinion,member, and means bridging the clutch member and pinion for determiningthe .maximum amount of spacing therebetween. o

8. In an engine starter drive, the combination of a prime mover, a pairof differentially threaded members mounted 'to rotate with said primemover, apinion having screwthreaded engagement with one of said members,and a clutch element having screwthreaded engagement with the other ofsaid members, whereby simultaneous rotation ofsaid threaded members willproject said pinion to driving position and move the clutch elementrelative to the pinion into clutching engagement with the latter;

9. In an engine starter drive, the combination of a 'primemover, a driveshaft rotated 10. In an enginestarter drive, the combination of astarting motor, a drive shaft rotated thereby, a pair of differentiallythreaded members on said shaft,one being fixed thereto, a pinion havingscrew-threaded engage ment with one of said members, and a clutchelement having screw-threaded engagement with the other of said membersand movable by difierential screw action into and out of clutchingengagement with the pinion.

11. In an engine starter drive, the combination of a starting motor, adrive shaft rotated thereby, a screw sleeve fixed thereto, a secondscrew sleeve of lesser pitch frictionally mounted on said shaft, a coneclutch member screwed on the sleeve of greater pitch, and a pinionscrewed on the sleeve of lesser pitch and having a cone clutch portioncomplementary to that of said'member.

PHILIP. S. CLAUS.

